I use my wooden patchbox to store cleaning tools. Less stuff in the bag, less to rummage through when loading. A brass box, though I haven't tried it, seems perfectly designed to carry greased patches and I think would likely speed up the loading process considerably by eliminating several steps needed to retrieve a greased patch from a separate container carried in the pouch.
I feel strongly enough about the utilitarian side of boxes that I even prefer them on modern guns, and were I designing a gun that I expected to depend on for survival a box would be very high on my list of desirable features.
There aren't many Rev-War vintage rifles without a pox, either metal or wood, BTW. The "poor boy" style is largely a post-Revolutionary thing.